1979 Mercedes Unimog 406 Barn Find

They are 3400-3500KG's but weighted to 5800KG my plan is to replate it so it can 100% legit be run  on a car licence without grandfather rights.

I think changing the tax class could open a real can of worms, you can run a tractor for fun legally on the road but not on red diesel unless you are involved in agricultural operations.
Also it is no longer going to be MOT exempted if you change the tax class and it's normally difficult to get agricultural stuff to meet the specs they will want.

I would get it in writing. The above is the standard advice from ploughing societies we've been involved with over the years including the tractor clubs who ensured that it was still legally possible to use rebated kerosine on the road in TVO tractors even when not involved in agricultural activities.
There's is absolutely 100% no requirement to own land, you may be thinking of the old limited use exemption which allowed you to do 5? miles a week but only cruising from one parcel of land you worked to another.

Guessing at the hydraulic valves. They look like diverter valves, so pressure/return in and one way or another after that. Will either in effect switch off the tipper or lift arms and switch on the extra service at the rear. Trailer tipper etc.
Looks like a good buy, it is the one I wish I had. Got a cheap ex military 406 but it was a canvas cab and the body was quite big which made it quite a numb thing in a tight spot.

You obviously managed to speak to someone helpful at DVLA. My dad bought a Massey Ferguson 135 that was on exemption and ended up calling them to try and sort the tax out. He’d had a letter to say they’d fine him if he didn’t tax it, but they couldn’t tax it as it was on exemption! Eventually got through to someone helpful and he managed to sorn it, but changing the class is still on the to do list.
Love the Unimog, they’re an amazing bit of kit

Right from the outset of this post, I had a niggling feeling that this Unimog in its current format was going to pose problems. I do not want to be a Jobs Comforter, but agricultural vehicles can be an absolute nightmare. Merely stating that this vehicle is an agricultural derivative, and not being involved in farming, horticulture, forestry etc..., means that white/standard diesel will have to be used. Finish of argument, and don't upset Customs as they can come along, dip the tank; on finding red-diesel they are empowered to seize the vehicle, end of story. In reality they tend to then calculate how much red-diesel you have used and fine you accordingly. You will then be given the opportunity to buy the vehicle back. I would suggest that for starters www.gov.uk/guidance/agricultural-vehicle-licences-and-fuel may well be a good place to start.
Changing the classification of the vehicle to a 'Goods Vehicle' will involve testing, etc... and again a complete nightmare. Dependant upon 'plated-weight', will dictate the class of driving licence required, etc...
You one option would be to trailer this vehicle to and from 'Trials-Venues', which then would require a suitable trailer, more than likely having air-brakes, and a suitable towing vehicle, possibly being an LCV in it's own right with the appropriate driving licence issues.
I wish you well, but this is a complete can of worms and not for the feint-hearted. The most sensible advice to date is emanating from raumer; in my opinion his input should be taken very seriously.

Thank you for the response; I still wish you good luck with your endeavours, and await the outcome with interest.

Epic build in the making. I have a soft spot for Unimogs. I remember the Belgian Army still had these in the late 80's.

My biggest issue at the moment is actually putting a value on all the stuff I'm taking off. Its all had alot of interest but no one seems to have an idea on value. Ive had atleast 10 messages with several guys wanting everything, but only one guy knowing enough to offer something for the rear linkage. It looks like they will go some way to ensuring funds for the restoration of the Mog.